As a conventional system for detecting an obstacle with a sensor mounted on a vehicle, a system disclosed in Patent Document 1 is known, for example. The system detects the vehicle behind and the like in a blind spot of door mirrors with ultrasonic sensors mounted on the door mirrors while driving, and operates as a vehicle monitoring (antitheft) system by monitoring an object near the sides of the vehicle while the vehicle is stopped.
On the other hand, an obstacle detecting apparatus of an automated guided vehicle described in Patent Document 2 time-shares a detection area of a ultrasonic sensor in a forward space of the automated guided vehicle, and makes a decision as to whether detection signals include noise or not from the number of areas from which the detection signals are obtained. Since acoustic noise has a high sound pressure level, it is received by the ultrasonic sensor as signals from a lot of detection areas. Accordingly, deciding the signals which are received from a lot of detection areas as noise makes it possible to prevent misdetection due to the acoustic noise.    Patent Document 1: Japanese Patent Laid-Open No. 10-100795/1998    Patent Document 2: Japanese Patent Publication No. 8-27342/1996
The conventional system decides that when the detection signals are present in one to two areas among the time-shared areas, they are normal, and that when the detection signals are present in three or more areas, they are noise.
However, it does not consider the continuity of the detection signal occurring in each detection area (the continuity of the detection signal in each search processing), which presents a problem of being unable to decide accurately as to whether the detected obstacle is a moving obstacle or not.
In addition, the conventional system is likely to make an erroneous decision that a static obstacle is a moving obstacle when the ultrasonic echo signals vary periodically as in the case of branches and leaves of a tree swayed in the wind. Thus, the conventional system has a problem of being unable to distinguish a moving obstacle such as a person from a static obstacle such as a tree accurately.
The present invention is implemented to solve the foregoing problems. Therefore it is an object of the present invention to provide a moving obstacle deciding apparatus capable of making a decision as to whether the search target is a moving obstacle or not accurately.